update README: documentation & contributing

Author: gourlaysama

README.md

@@ -1,10 +1,15 @@
 scala-parser-combinators [<img src="https://api.travis-ci.org/scala/scala-parser-combinators.png"/>](https://travis-ci.org/scala/scala-parser-combinators)
 ========================
 
-Scala Standard Parser Combinator Library
+### Scala Standard Parser Combinator Library
 
 As of Scala 2.11, this library is a separate jar that can be omitted from Scala projects that do not use Parser Combinators.
 
+## Documentation
+
+ * [Latest version](http://www.scala-lang.org/files/archive/api/2.11.2/scala-parser-combinators/)
+ * [Previous versions](http://scala-lang.org/documentation/api.html) (included in the API docs for the Scala library until Scala 2.11)
+
 ## Adding an SBT dependency
 To depend on scala-parser-combinators in SBT, add something like this to your build.sbt:
 
@@ -15,3 +20,8 @@ libraryDependencies += "org.scala-lang.modules" %% "scala-parser-combinators" %
 (Assuming you're using a `scalaVersion` for which a scala-parser-combinators is published. The first 2.11 milestone for which this is true is 2.11.0-M4.)
 
 To support multiple Scala versions, see the example in https://github.com/scala/scala-module-dependency-sample.
+
+## Contributing
+
+ * See the [Scala Developer Guidelines](https://github.com/scala/scala/blob/2.12.x/CONTRIBUTING.md) for general contributing guidelines
+ * Have a look at [existing issues](https://issues.scala-lang.org/issues/?filter=12606)